Engines for propulsion systems, e.g., aircraft intake air for operation. The air needs to be contaminant-free for efficient engine operation, e.g., internal combustion. Moreover, contamination of intake air can cause internal damage, e.g., premature wear on engine components resulting in increased maintenance costs and decreased operational reliability. When aircraft operate at low altitudes or idle on the ground, or in icing conditions, the engine can be exposed to contaminants. A filtration system can be placed at an engine inlet to filter the intake air. The filtration system can eliminate contaminants by providing substantially contaminant-free air for engine intake.